Transistor device with self-jigging construction



Nov. 3, 1964 KELLEY 3,155,936

TRANSISTOR DEVICE WITH SELF-JIGGING CONSTRUCTION 2 Sheets-Sheet 1Original Filed April 24. 1958 INVENTO DALE 7? K51 BY MW AYTORNEY Nov. 3,1964 D. T. KELLEY 3,155,935

TRANSISTOR DEVICE WITH SELF-JIGGING CONSTRUCTION Original Filed April24, 1958 2 Sheets-Sheet 2 LLOAD BASE CONNECTOR 2. LOAD BASE SOLDER RING3. LOAD mcs j 4. CLOSE a FASTEN aoAT X 104 105 WORK FEEDER LOADCOLLECTOR ALLoY COLLECTOR BEADS IN BOAT SIDE a BAsE (BEAD LDADER)CONNECTION 109 (FUSION FURNACE) 112 107 BOAT L BOAT a INVERTINGINVERTING ES STATION STATION ALLOY EMITTER LoAD EMITTER SIDE (FUSIONBEADS IN BOAT FURNACE) (BEAD LOADER) BOA INVERTING STATION LOADCOLLECTOR SOLDER WIRES LOAD EMITTER WIRES IN BOAT (FUSION FURNACE) WIRESIN BOAT (WIRE LOADER) VIBRATOR (WIRE LOADER) MOUNTED LoAD HEADER UNLOAOa-Hon FURNACE SUB-ASSYS I 11 FROM BOAT TRACK L SOLDER wmzs (FUSIONFURNACE) 121 122 VIBRATOR 7 2 MOUNTED DROP suB-AssYH a a n Y ,%F= SOLDERmass :1

ON HEADER I I Tl SOLDER SUB-ASSY T0 HEADER (FUSION FURNACE) -VACUUMBAKED -ETCHED -BACK FILLED 4 -WASHED 'PIN HOLE SEALED -CHECKED INVHVTOR.-FINAL TEST -CANNED DALE rkfufy v ey mm'imeu m 7 ATTORNEY United StatesPatent 6 Claims. (Cl. 338-329) This invention relates to manufacturingand structural improvements in the semiconductor art, wherein thedevices produced for use in electronic equipment are of diminutive size,and more particularly to alloy junction transistors of such size, aswell as to an improved method for making such devices, and to apparatusfor practicing such method. The invention provides a highly mechanized,efficient and economical assembly operation and a device which lendsitself to mass production, while permitting changes in the semiconductorsubassembly within the device to permit a ready change to many differentpredetermined operating characteristics for the device which make itpossible to adapt the same to many different equipment applicationspecifications. This flexibility is accomplished by the presentinvention with only minor changes in the process, manufacturingapparatus, and device structure itself. I

This application is a division of a copending application of Dale T.Kelley, Serial No. 730,642, now abandoned, filed April 24, 1958, andassigned to the present assignee.

In order to obtain certain electrical characteristics such as good highfrequency response, it is desirable, in the present state of the art, tomake a transistor quite small, or one might say, relatively minute. Themanufacture of such relatively minute devices poses many practicalfabrication problems due to the size of the articles being assembled.Since a transistor normally includes several separate parts, theassembly process involves the alignment and connection of such parts inan accurate and uniform manner. ecause the parts being assembled oftenhave dimensions of only a few hundredths or even thousandths of an inch,their accurate positioning is extremely difficult. For example, certainalloy junction transistors include a wafer or die of a semiconductormaterial such as silicon or germanium which carries on its oppositefaces minute electrodes of an impurity metal such as indium. Theelectrodes must be positioned accurately directly opposite one anotheron the germanium or silicon die, and then heated so that they will fuseto the surface of the semiconductor die and alloy into it a controlleddistance in order to create two suitable rectifying junctions. Suitablelead wires must be electrically connected to each electrode in order toconnect the device into a circuit. Since the diameter of the electrodesis often in the order of about 0.01 inch, it is difficult to align themdirectly opposite one another and it is equally dinicult to position thelead wires accurately and secure them to the electrodes.

For instance, in a device wherein a semiconductor die carrying alloyedelectrodes is connected to a mounting to form a subassembly which inturn is secured to the posts of a mounting header for the completedevice, the small size of the parts involved, makes proper alignment ofthe subassembly with the header posts difficult. its successfulaccomplishment in prior practices requires the use of expensive specialjig and assembly equipment such as lead attaching pantographs whichgreatly reduce applied motion and thus permit relatively accuratepositioning of the component parts, and prior practices require skilledlabor when they are assembled by hand. Such hand assembly methods areslow and add materially to production costs. Of equal, or possibly ofgreater importance, is the matter of producing relatively minutesemiconductor devices in the large commercial quantities required, andattaining uniformity in assembly and in operating characteristics for aparticular design. Failure to solve this problem in this art has keptthe manufacturing yield rate low, and kept the cost of the acceptedunits high.

Accordingly, it is a highly desirable objective to eliminate handassembly and utilize mechanized or automatic assembly techniques in themanufacture of semiconductor devices such as transistors, but theaccomplishment of the objective has left much to be desired in the past.

Another highly desirable objective in semiconductor device manufactureis the standardization of assembly procedure and equipment. At present,most commercial assembly procedures and equipment are relativelyinflexible and can be used to manufacture only one or a few specificdevices. Since the state of the art is advancing quite rapidly, theyquickly become obsolete. Consequently, substantial savings in capitalinvestment for new equipment could be made if the same or slightlymodified equipment could be used in the manufacture of devices havingdifferent types of semiconductor die units and consequently differentoperating characteristics for equally different applications inelectronic equipment. This is particularly important in this art,because relatively it is in its infancy and electronic equipment must bedeveloped to utilize the semiconductor devices. With the development ofequipment new devices are required. In all, it is a rapidly advancingart where there has been great obsolescence in methods, manufacturingapparatus, and devices as the art advances.

There could also be a substantial reduction in manufacturing costs ifthere could be some standardization of parts which could be used withmany devices with different characteristics so as to require only onetype of assembly equipment for all such different devices.

Another factor tending to increase the cost of semiconductor manufactureis the loss of expensive component parts when rejected transistors orother semiconductor devices are destroyed. In many transistorconstructions, for instance, both the mounting header and the die unitmust be discarded if the transistor fails to meet electricalspecifications. In the great majority of cases, however, failure of atransistor to pass electrical specifications is due to some defect inthe semiconductor die unit rather than to any defect in the mountingheader. The mounting header is an expensive component of the transistor,but entirely satisfactory ones must be discarded if it is not possibleto easily and quickly remove a faulty semiconductor die unit, when thetransistor fails to meet the specifications in a stage of assembly priorto final canning. Such mounting headers would be suitable for reuse withother semiconductor die units, however, if they could be easily detachedfrom the faulty die unit.

in the manufacture of alloy junction semiconductor devices, wherein theinternal dimensions between alloyed junctions on the semiconductor dieare critical, the penetration of the alloyed electrode into the dieduring alloying is material. This alloying penetration or depth dependsupon alloying temperature, volume of alloying metal present, and contactarea between the metal and the semiconductor die surface. ll/hen twoelectrodes, such for instance, as an emitter and a collector are alloyedto a die simultaneously and at the same temperature, it has provendifiicult to control accurately the alloying depths of both electrodesand the internal dimension between the junctions. However, the art hasconsidered that simultaneous alloying was necessary to economize timeand handling and hence minimize production costs.

It is an object of this invention to provide a method of assemhlingsemiconductor devices, which method is characterized by greatflexibility and by rapid and simple adaptation to the manufacture of avariety of different devices, and particularly to the manufacture of lowand medium power transistors with alloy junctions, so that the samemethods and assembly apparatus can be used over a substantial period oftime in this rapidly advancing art as changes are made in the operatingcharacteristics of structure of the devices.

A further object of this invention is to provide a manufacturing processand apparatus for diminutive alloy junction semiconductor devices whichaccomplishes mass production and low cost but a higher yield at thecompletion of the process than has been possible in the past.

Another object of the present invention is to provide a transistoradapted to be manufactured economically, uniformly and at a high rate ofproduction.

A further object of the present invention is to provide a transistorstructure which lends itself to relatively quick and easy assembly ofits minute component parts by the use of relatively simple apparatus soas to maintain capital expenditures for apparatus at a minimum.

it is another object of the invention to provide an improved transistorwhose structure not only lends itself to manufacture by automaticassembly techniques, but is also standardized to a degree such that asubstantially identical mechanical mounting will make possible numerouspredetermined and different electrical operating characteristics indifferent transistors.

It is another object of the present invention to provide an improvedtransistor structure from which electrically defective semiconductor dieunits can easily be removed thus enabling the reuse of the mechanicalmounting base portion with other die units and the consequent salvage ofthe cost of such base portions.

A feature of this invention is the provision of a method of assemblingalloy junction transistors which improves the accuracy with whichelectrodes may be positioned on a semiconductor die and suitable leadsaffixed to the electrodes so as to provide a uniform product coming froman assembly line, and accomplish a high yield and lower costs ofmanufacture while speeding up the required full production time relativeto the yield accom- I plished.

Another feature of the invention is the provision of a devicesubassembly made up of a base connector strip and a semiconductor dieunit mounted thereon which becomes self-jigging when assembled on fourposts or the posts and connector leads on a mounting header. The baseconnector strip is provided with a pair of arms having engaging meanssuch as hooks formed in their ends for engaging upright posts of amounting header and enabling the subassembly to be quickly and easilypositioned on the header at the posts for soldering thereto. Angularlybent lead wires or posts in the header support and position small wireleads from the electrodes on the semiconductor unit. Because the hookshold the subassembly against lateral movement, and the pieces settleinto a final position on the angularly bent leads and on the straightposts during heating for soldering, and because of the prior applicationof solder material at the connections to be made, soldering to theheader can be carried out quickly and effectively on an economical massproduction basis.

Still a further feature of the invention is the off-center mounting ofthe semiconductor die unit on the aforementioned base connector andconsequent off-center weight distribution of the center of such unit sothat lead wires extending from the die unit rest on and slide along theaforesaid turned-over or angularly bent ends of the header mountingposts or leads as the suhassembly settl s into position on the header.Each post or upright lead is on-center in the header and the fourprovided in one embodiment are equilaterally placed therein, but

a the turned-over or angularly bent portion of each is offcenter and thesubassem ly lead wires rest on the same. This construction anddimensioning assures that contact is maintained between the subassemblylead wires and its connector strip and the mounting posts duringsoldering of the subassernbly to the header, and prevents the productionof devices wherein the parts are imperfectly connected by solder to theheader.

In the accompanying drawings:

PEG. 1 is a greatly enlarged view in perspective of a transistor of thepresent invention with its cover member broken away to show its internalstructure;

FIG. 2 is an exploded view of the transistor shown in PEG. 1, with thesame enlargement to better illustrate the components making up the unit;

FiG. 3 is an enlarged perspective broken view of one end of each half ofa heat resistant jig or boat employed for guiding the pieces to besecured together by fusion or alloying into the semiconductor die unitin an assembly step of the present invention, showing the two halves ofthe jig in open position;

FIG. 4 is a fragmentary view in section through a closed jig of the typeshown in FIG. 3, but enlarged over the showing in PEG. 3, andillustrating the dropping of a minute metal bead toward one face of asemiconductor die;

PEG. 5 is a view similar to FIG. 4 showing the dropping of the otherelectrode bead toward a position on the opposite face of thesemiconductor die;

FIG. 6 is a view in section similar to FIGS. 4 and 5 showing thepositionin for affixing of a lead wire to one of the electrodes which isthen alloyed onto a face of the semiconductor die; and

FIG. 7 is a flow sheet illustrating the various steps of the assemblyprocess and showing assembly equipment in diagrammatic form.

In practicing the present invention as directed par ticularly to amethod for making alloy junction devices such as so-called transistorsand such devices resulting therefrom, i provide a production line overwhich manufacturing steps are accomplished with a maximum ofautomatically operated equipment of apparatus and a minimum of handlabor to provide mass production of these diminutive or relativelyminute devices wherein a high degree of uniformity in structure andelectrical operating characteristics are accomplished. This in turnprovides a high yield in terms of acceptable units cor ing from the massproduction operation.

The minute parts of a semiconductor subassembly are assembled in largemultiples and primarily by automatically operated apparatus into heatresistant jigs which are then each moved into fusion furnaces for theheating and fusion together of semiconductor subassemblies. Thecollector and emitter electrodes and the wire leads extending therefromare the most critical so far as the position thereof on thesemiconductor die and so as the fusion thereof together are concerned,and accuracy of position and complete fusion are accomplished by loadingand then fusion of first one electrode and then the other, and thenloading and fusion of one wire lead on an electrode and thereafter theother wire lead on the other electrode; In this manner each handling ofa piece or part can be brought up to maximum efficiency and each of thefour fusion furnaces used for the two electrodes can be provided with anatmosphere and a temperature to accomplish the best fusion conditionsfor the different electrodes.

After completion of the subassembly, and at subsequent loading positionsin the production line, the mount ing member or header for thesemiconductor devices such as a transistor, and the semiconductorsubassembly are placed together and this is automatically moved into afifth fusion furnace for soldering together which accornplishes theassembly of all mechanical parts of the: device except the final coveror can.

With the mechanical assembly complete, each device in this stage ofcompletion is automatically electrolytically etched for cleaning, iswashed to remove the solution, and electrically tested. Then a cover isplaced on those assemblies which have not been rejected at theelectrical testing stations for unacceptable characteristics orinoperativeness.

This invention also includes an improved device-structure whichemphasizes the effectiveness of the process and apparatus justdescribed. The semiconductor subassembly for such device includes a fiatenlarged metal strip which not only serves as part of the mechanicalmounting means for the subassembly on a mounting header as well as anelectrical connector, but lends itself to the production of a pluralityof subassemblies in an improved single heat-resistant jig. A pluralityof such strips are placed in the jig and quickly aligned in a properposition so as to receive first a semiconductor die on each strip, andthen metal electrode beads to be fused thereto, and lead wires to befused to the electrodes so that electrical connections can be made tothe semiconductor subassembly. The connector strip serves to mount asemiconductor die and additionally includes hooks on each end by whichthe final subassembly can be readily and simply positioned oncorresponding posts of the mounting header.

The mounting header also represents an advance in the art of commercialimportance in that four posts are equilaterally mounted therein and twoof the four posts on the header are bent over at an angle to receive thewire leads from the subassembly while the connector strip hooks arepositioned on the straight posts to center that element, wherein thesubassembly is held in position on the header prior to and during finalsoldering. The four posts are insulated in the header from a metalcovering, and an insulating portion between the straight posts extendsthrough such covering and between such two posts so that the strip willnot be short circuited with the covering. In this respect, theconfiguration of the connector strip in combination with the header alsofacilitates the final assembly. The semiconductor die on the strip isoif-center. Although the four posts in the mounting header are securedtherein in an equilateral position, the off-center arrangement of thesemiconductor die on the connector strip insures that the thin wireleads extending in opposite directions from the electrodes thereon restsecurely in the extended turned-over portion of each of two of theposts. Each such portion slopes toward the base portion of the postwhich is in the equilateral position described. As a result, thepositioning of the semiconductor subassembly on the mounting header canbe rapid because of the tolerances provided by the length of eachturned-over portion. Solder material is at the joints and thesubassembly settles down the sloping portion into a rigid predeterminedposition on the header when the solder is melted in the fifth fusionfurnace.

Not only does the complete mechanical structure of the device of thisinvention lend itself to quick and accurate assembly without jigs exceptthe heat resistant block unit, but this same structure and the solderedconnections of the subassembly to the header make it possible to heatand unsolder this subassembly from the header if the final electricaltest before canning shows the subassembly to be unacceptable from anelectrical and operating standpoint. Being able to salvage the headerrepresents a substantial saving in cost of manufacture, and adds toother savings represented in the complete embodiment of the invention.

FIG. 1 of the accompanying drawings shows a perspective view of acompleted transistor of the present invention with the cover portionbroken away. PEG. 2 is an exploded view of the same transistor moreclearly showing its component parts. The transistor generally indicatedat It) includes a mounting header 11 which comprises a disclike member12 of glass or other suitable insulating material covered with a sheetof metal such as the alloy Kovar except for the areas immediatelyadjacent tie mounting leads or posts and an elongated area between twoof the posts. Passing through the glass disc and supported therein arethe header mounting leads or posts including the emitter lead or post13, the collector post 14, and the base post 15. A fourth post 16 alsois held in the header but does not pass completely through it as do theother posts, and serves no electrical purpose but acts merely as aconvenient mechanical support. The posts 13- 16 are of a suitableconductive metal or alloy such as an iron-nickel alloy which can besealed to the insulating material of the mounting base.

The subassembly generally indicated at 17 is mounted on the posts 134.6and is made up or" the base connector and die supporting member 18 whichitself comprises a round enlarged or extension portion 19 and extendingarm portions ill and 21. Arm 2% is somewhat longer than arm 21. Theportion 19 of the base connector 18 is provided with an opening 1%. Thearm 26 is provided with a hook member 22 adapted to engage the base post15 and is soldered thereto. Soldering may be accomplished with a solderring 23 (shown in FIG. 2) or by other solder applications lendingthemselves to mass production. The arm 21 is provided with a pair ofhooks 24 and 25 which engage the post 16 and are soldered to it by meansof a solder ring 26, or other suitable soldering as described for theconnection on post or lead 15. The base connector member, in accordancewith one embodiment of the present invention is made of anickel-containing alloy Kovar. However, other suitable conductivematerial may be used having about the same thermal coeficient ofexpansion as the semiconductor die and to which the die can convenientlybe connected. Metallic nickel is a suitable material.

The subassembly 17 also includes the semiconductor water or die 27 whichis secured to the enlarged portion 1 along the periphery of opening 1%by means of the solder ring 2i which is made of solder of high leadcontent. The die 27 fits over the opening 19a and carries on its facesmetal beads which serve as electrodes. The bead 29 serves as the emitterelectrode of the transistor while the head 36 serves as the collectorelectrode. The subassernbly 17 is arranged with emitter electrode 29extending into opening 19a. Emitter lead 31 is fused to emitterelectrode 29 while collector lead 32 is similarly secured to collectorelectrode 30.

The leads 31 and 32 from the subassembly 17 rest on the overturned orsloping ends of posts 13 and 14 respectively, and are soldered to themby a suitable production means as by the melting of solder preforms 31aand 52a.

The structure of the transistor in makes it well adapted to manufactureby automatic assembly techniques, and is suitable for any one of avariety of low or medium power transistors in which the amount of heatgenerated at the rectifying junctions is small enough to be successfullydissipated through wire leads. Once the subassembly 17 has beenseparately fabricated, the attachment thereof to the header 11 may becarried out expeditiously in a manner to be described subsequently.However, because of the very small size of the component parts of thesubassembly (the overall length of the base connector 18, for example,in one embodiment of the invention is only about 0.200 inch) specialtechniques are employed which provide for its quick, accurate andeconomical manufacture. Accuracy of assembly is particularly importantsince electrical connection is made through the very fine wire leads 31and 32, which in turn are fused to the very small electrode beads 29 and3% FIG. 7 shows in diagrammatic for-m a flow sheet of the various stepsof the method of fabricating the subassembly 17. The first step in thisprocess is the positioning of the base connector 18, the solder ring 28and the semiconductor die 27 in the jig generally indicated at 33 inFIG. 3. This step is accomplished at the loading station 101 on FIG. 7.Solder ring 28 is preferably dipped in a mixture of ammonium chlorideand alcohol to provide a flux. The jig 33 is composed of blocks 34 and355 made of graphite, steel or some other suitable material capable ofwithstanding heat. The block 35 has formed therein a number ofdepressions indicated generally at 37 in its face 36, and shaped toaccommodate the base connectors 13. The depressions are interconnectedso that a number of connectors may be placed end to end to increase thenumber of subassemblies fused or alloyed together at the same time. Aboss 38 is provided to accommodate the opening 19a formed in the centralportion 19 of the base connector. Each boss member 38 is provided with acentral passage 39 which passes all the way through the block 35providing access to the interior portion of the jig when it is close Theblock 3 has an essentially fiat surface with passages 46 passingcompletely through the block and adapted for alignment with passages 39when the jig is closed by placing surface 41 of block 3 on surface 36 ofblock 35.

Transverse grooves 41a accommodate the hooks of connector 318. The block35 is provided with a peg 42 which fits into opening of block 34 whenthe jig is closed. The two halves of the jig are secured together by ascrew or bolt passing through holes 44 and 45.

After a series of base connectors 18 have been placed in block 35 of thejig 33, a solder ring 2% (FIG. 4) is placed on each base connectoraround the opening 1k: and a semiconductor die 27 is placed on thesolder ring. The semiconductor die 27 is made of germanium or silicon ofsuitable conductivity type and of predetermined resistivity andelectrical characteristics. ln'a specific embodiment of the presentinvention, the die 27 is of N conductivity type germanium.

The jig 33 is closed in the manner previously described and passes alongconveyor means 1% to the collector electrode insert station TM. Acollector electrode bead Ell is dropped through the passage 4% as shownin FIG. 4 and falls onto the surface of die 27. The mouth portion of thepassage 4b is somewhat enlarged to facilitate insertion of the beadalthough its bottom portion is of suffici'ent width to just accommodatethe bead thus guiding it into place and assuring accurate positioning onthe surface of the semiconductor die 27. In accordance with a specificembodiment of the invention, the collector bead 30 is composed of indiumalthough other suitable acceptor impurity metals which will alloy intothe N conductivity type to form a suitable PN junction may also beemployed. For example, when using a semiconductor die of N-typegermanium, as in the embodiment particularly described, other alloyingacceptor metals such as gallium or zinc or alloys of these metals withindium may be used. in the event P-type germanium or P-type silicon isused in the semiconductor die, a donortype alloying impurity, such as anantimony alloy, forms the electrodes. A specified amount of ammoniumchloride-alcohol fiuxing solution is introduced through passage ltl toassist in alloying collector bead 30 to die 27.

The jig 33, now containing, in accordance with one embodiment of theinvention, sets of parts, each set includ ing thebase connector 1%, thesolder ring 28, the semiconductor die 27 of N-type germanium, and theindium collector bead Fall, is placed in the magazine of the collectorfurnace MP5. Successive jigs are moved through the furnace (inaccordance with one embodiment of the invention) by the action of apneumatic pusher which pushes the last-inserted jig from the magazinecausing it to displace the next preceding jig along the furnace. in thefurnace, the assembly is heated to melt the solder ring and thusattached the semi-conductor die 27 to the base connector 13. The heatingalso melts the indium collector bead S-tl and causes it to alloy intoand fuse with the semiconductor die 2'7. This creates a region of P-typeconductivity beneath the surface of the semiconductor die 27 and createsa PN rectifying junction within the die.

The electrical characteristics of an alloy junction type transistor aredetermined to a considerable extent by the depth of alloying thecollector and emitter electrodes since this controls the distancebetween the PN junction in the semiconductor die. This alloying depth isdetermined by the volume of alloying material available, the area wet bythe alloying material and the alloying temperature. The collectorfurnace tee is an electric resistance furnace containing an atmospherethat is inert with respect to the material making up the transistor. Ingeneral, such atmospheres are reducing or non-oxidizing. Nitrogen,argon, or a mixture of nitrogen and hydrogen are suitable atmospheres.The temperature maintained within furnace ms is dependent upon theelectrical characteristics to be produced in the transistor since theseare, to at least some extent, controlled by the depth of alloying of theindium. in accordance with the present invention, temperatures betweenabout 400 and 700 C. are employed, with high temperatures being usedwhen greater alloying depth is required. In one embodiment. of theinvention, a temperature of about 580 C. is employed in the collectorfurnace. in one embodiment of the invention, the total residence time ofeach jig in the furnace is about 15 minutes with a jig leaving thefurnace every 30 seconds. This provides sufficient ttime to obtainequilibrium alloying at the temperature specified. There is no practicalupper limit on the heating period since once the alloying of the indiumand germanium is accomplished at a particular temperature, it will notproceed further unless the temperature is raised.

The jig 33 is moved from the cooling chamber of furnace M5 to thejig-turning station lltll where it is inverted either manually or bysuitable mechanical means so that the block 35 of the jig is now facingup. The turned jig then passes to the emitter insert station M98 and theemitter electrode head 29 is dropped through the passage 59 (FIG. 5) sothat it rests on the surface of the semiconductor die 27 directlyopposite the collector electrode Bill. in maldng transistors in whichthe emitter electrode is somewhat smaller than the collector electrode,the passage 39 is of somewhat smaller diameter than the passage ltlthrough which the collector bead 3th was dropped. The passage 39 is alsoflared at its mouth to make insertion of the electrode bead easier andis narrower near its bottom so that it will serve to properly positionthe indium bead on the surface of the semiconductor die. As in the caseof the insertion of the collector bead, the emitter bead is inserted bythe mechanical insertion means of FIG. 8 to be described subsequently. Apredetermined amount of the ammonium chloride-alcohol fluxing solutionis introduced through passage 39 onto bead 29.

The loaded jig 33 then passes to emitter furnace res which is identicalwith collector furnace 1% and employs the same atmosphere, but it ismaintained at a somewhat lower temperature to provide for less alloyingpenetrationof the emitter than the collector. For example, in theembodiment of the invention employing a temperature of 580 C. in thecollector furnace, a temperature of about 520 C. is employed in theemitter furnace. Once the alloying of the collector bead has beencompleted to equilibrium in furnace M35, subsequent exposure of thecollector to a lower temperature will in no way affect its alloyingdepth. if both the collector and emitter electrodes were fused to thesemiconductor die in the same furnace at the same temperature, thattemperature would determine the depth of alloying whereas, in accordancewith the present invention, where alloying is carried out in twoseparate furnaces, at two different temperatures, well controlled depthof alloying can be obtained for the emitter by first fusing thecollector electrode to the die at a somewhat higher temperature. in manyapplications of the invention, such as in the manufacture of diffusedbase transistors, very shallow alloying is desired for the emit terwhile deeper penetration is desired for the collector. This isaccomplished by first alloying the collector to the desired depth andthen allo ing the emitter to a lesser depth at a lower temperature sothat it does not affect the depth of alloying at the collectorelectrode. Once the collector has alloyed to its equilibrium depth at aparticular temperature the alloy region will not penetrate furtherunless that temperature is exceeded.

Independent control of alloying depth of the electrodes in the presentmethod and apparatus also permits accurate control of the distanceseparating the two PN junctions in the semiconductor die or so-calledbase width of the PNP transistor. This dimension has an important effecton the electrical charcteristics of the unit. Because of the independentcontrol of each alloying step the process can be used to manufactureunits of different electrical characteristics by varying the alloyingtemperature. Although the atmosphere and residence time employed the twoelectrode alloying furnaces are normally the same, they could be variedif required.

Although the foregoing description has referred specifically to aparticular type of alloying and particular ma terials, it will beunderstood that the process of the invention can be easily modified toform other types of alloy junctions. For example, the operatingconditions of the alloying furnaces could be modified to heat asemiconductor die upon which a metal had been deposited, as byevaporation, and form a so calle-d toasted alloy junction. in such amodified process, the same base connectors, jigs and the like could beused as are employed in the embodiment described in detail. Further, itwill be understood that semiconductor dice employed may be of eitherconductivity type, may contain regions of varying resistivity as in thecase of graded base transistors, or may have whatever electricalcharacteristics are required to produce a predetermined device.

After the alloying of the emitter electrode 29 has been completed, thejig is turned over at the inverting station 111 and passes to thecollector lead insert station 112. At collector lead insert station 112,a collector lead wire 32 is inserted through each passage 4-0 either bya wire loading mechanism which cuts the leads to length and lock themautomatically or by hand, and allowed to rest with its end held againstcollector electrode 3%) by gravity (FIG. 6). The collector lead wire 32is made of gold-plated silver because of the ease with which indium andgold Wet one another so that they can be electrically connected merelyby making contact and heating. Unplated silver wire also may be employedbut higher temperatures are required. Positioning of the lead wire 32 isaccurate because it is guided by the bore of the passage 40 andautomatically positioned thereby on the surface of the collectorelectrode 30. As shown in FIG. 6, lead Wire 32 is of such a length thatit does not extend beyond the outer surface of the jig. This permitsinsertion of the jig without disturbing the position of the lead.

The jig with the lead wire 32 inserted therein is then passed by apneumatic pusher to collector lead furnace 113 which is also an electricresistance furnace contain ing a neutral or nonoxidizing atmosphere andmaintained at a temperature between about 300 and 406 C. In oneembodiment of the invention, a temperature of 380 C. is employed. Atthis temperature the lead 32 readily fuses to the indium electrode 30and is mechanically affixed and electrically connected thereto. The leadwires are about one-half the diameter of the electrode to which they arefused. It has been observed that they are well centered with respect tothe electrodes and this is believed to be due to the surface tension ofthe indium as it becomes molten during the fusion process. The residencetime in the collector lead furnace is substantially the same as that ofthe two electrode furnaces.

After the attaching of the collector lead the jig passes invertingstation 115 from which it passes to the emitter lead insert station 116.At this point the emitter lead 31 is inserted into the passage 39 inexactly the same way as the collector lead 32 was inserted into the pas=sage 4t), and the jig passes to the emitter lead furnace 117 where thesilver emitter lead wire is fused to the indium by heating under thesame conditions as obtained in the collector lead furnace 113. The jigand its contents are then cooled, and the completed subassemblies 17 areremoved at station 113 by opening the jig and separating the blocks.

In some instances it has been found desirable to provide means forvibrating the jigs after the leads have been inserted and before theyare fused to their corresponding electrodes. Such vibration prevents theleads from becoming stuck in the jig openings in positions where theyfail to contact the electrodes, and it generally provides for moreeffective lead attachment. This may be accomplished by mounting the leadattaching furnaces 113 and 117 so they can be vibrated, and it isindicated in FIG. 7 by reference inasmuch as the details are not a partof the present invention.

In the embodiment of the invention particularly illustrated, theattachment of lead wires to alloyed electrodes is described. It will beunderstood, however, that the method and apparatus of the invention maybe used to attach lead wires to other types of contacts eitherrectifying or ohmic with the same resulting advantages of ease andaccuracy of positioning, reproducibility, high production yield andeconomy. For example, a semiconductor die having plated electrodes canbe positioned within the jig 33 with a base connector and solder ringand the jig introduced into the process at the wire loader 112. Leadattachment is then accomplished in the manner previously describedmaking such changes in furnace temperatures and the like as areexpedient for the particular materials employed. Similarly,semiconductor bodies having diifused or grown rectifying junctions andohmic contacts on their surfaces may have lead wires accurately attachedto such contacts in accordance with the present invention. Suchflexibility is one of the advantages of the invention since it enables awide variety of transistors to be manufactured using the same equipmentand general assembly procedures and thus tends to keep such equipmentfrom becoming obsolete as transistor structures and characteristics areimproved.

The completed subassemblies are of a configuration which facilitatestheir quick and accurate alignment on a slightly modified standardmounting header having four equilaterally spaced mounting posts. Asindicated in FIG. 7, headers 11 are loaded in an upright position onto amoving conveyor. belt or track 119 at station 129 and pass to theloading station 121. At this position, an operator or a suit-ableloading mechanism drops a subassembly onto a header with the hooks 24and 25 of the shorter arm 21 engaging the dummy or electrically inactivepost 16 and with the book 22 of the longer arm 24) engaging the basemounting post 15 (see FIG. 1). Shorter arm 21 is provided with a pair ofhooks to enable an operator to distinguish one end of the base connectorfrom the other and so orient successive subassemblies uniformly withrespect to the headers on which they are mounted. When the subassembliesare placed on the headers manually, the operator usually engages post 16first and then slips hook 22 around post 15.

As the subassembly is placed on the header, the emitter and collectorleads 31 and 32 contact the turnedover and sloping end portions ofemitter and collector mounting posts 13 and 14 respectively. The endportions are bent toward the shorter arm 21 of base connector 18 andform an angle of about 30 with the upper surfaces of the header.

The hooks at the ends of the base connector arms hold the subassembly 17against lateral movement with respect to the mounting posts and maintainit in proper alignment to be soldered to the header. This soldering maybe accomplished by a soldering iron, but is preferably carried out on amore rapid production basis by a preapplication of solder and thenheating and fusing in the furnace 122. In one embodiment, solder rings23 and 25 (FIG. 2) are dropped over posts 15 and 14 respectively ontothe hooks engaging these posts, and solder rings 31a and 32a are droppedover the turnedover sloping ends of posts 13 and 14 to rest againstleads 3i and 32 respectively. The resulting units pass along track 119(FIG. 7) to furnace 122 wherein the solder rings melt to form jointsconnecting the subassemblies to their headers mechanically andelectrically.

As the subassemblies are placed on the headers, they are roughlyoriented With the base connector arms substantially parallel to theupper surface of the header. As the solder rings melt, the subassembly155 will tend to settle into the stable position shown in FIG. 1 as thelead wires 31 and 32 slide along the bent-over end portions of posts 13and 14 respectively. Because the semiconductor die 27 is carried onconnector is in a position somewhat off-set from its center toward thesame direction in which the turned-over ends of posts 13 and 14 arebent, the lead wires extending from the die will make contact with theposts even if the subassembly is slightly misaligned, and the chance ofmaking a faulty connection to the lead wires is minimized. As the soldermelts, the angular disposition of the post ends insures contact by theleads to be maintained as the subassembly l8 settles into its moststable position.

As the subassembly 1S settles during soldering, the edge of the enlargedportion l9a engages the exposed surface of insulating body 12 and ismaintained in the stable position shown in FIG. 1. The provision of theexposed insulating area on the header surface for supporting the baseconnector 1? permits self-jigging of the subassembly 17 on a headerwhich is otherwise of standard design, this construction can be used tomount a wide variety of semiconductor subassemblies.

The shape of the exposed insulating area between posts 15 and 16prevents short circuiting of the base connector to the metal covering ofthe header since the connector will not contact the covering Ila even ifit should be mounted in a tilted position as with one of its armsresting on the header. The provision of the metal cover 11a over otherportions of the header body 12 improves electrostatic shielding of theunit.

It will thus be seen that the configuration of the base connector 18 andthe provision of the bent-over end portions of posts 13 and 14 enablesthe subassembly 17 to be self-jigging with respect to header 1]. so thatsolder connections can be made easily and accurately at a high rate ofproduction with a high yield of electrically satisfactory units. Becausethe subassembly is self-jigging, soldering can be accomplished byplacing solder rings or placing solder in some other manner on theassembly joints to be soldered and passing it through a furnace. Thisresults in cleaner, better aligned and more uniform units than could beproduced by manual soldering since manual soldering may cause smearingand dirtying and misalignment in handling to an extent that might resultin an unacceptable unit.

In addition to improving product yield and reproducibility, theinvention accomplishes these improvements in conjunction with asubstantial reduction of operators needed to maintain a given rate ofproduction. Thus, a reduction of 25% to 50% in the number of operatorsrequired for a given rate of production can be obtained by using thepresent invention instead of conventional manual assembly techniques.

Following the soldering operations, the units are removed from the belt119 and placed in individual carriers which hold the lower portions ofposts or leads 13, 14 and 15 in a fixed position and establishes areference surface for loading in sockets of an automatic etchingfacility shown at 123 in FIG. 7. The units are plugged into sockets on amoving belt and carried successively through an electrolytic etchingbath, a deionized water rinse, a pressurized air-water mist rinse, ahigh pressure air blowoff, a radiant heat drying position and anunloading position. The units then pass to electrical testing stationswhich may be provided with automatic sorting and ejection means.Although it is expedient to carry out the etching, Washing and testingsteps by the mechanized means described, the invention may also bepracticed with these steps accomplished by other means whethermechanized or not, and the specific mechanism used in the commercialembodiment of the present invention is not a part of this invention.

Assembly of the transistor is completed by the attachment of covermember 46. The cover is made of mild steel or nickel silver and whichrests on the lip or shoulder lib of header ill. The cover member 4-6 isaflixed to the header by welding to such shoulder.

In accordance with one embodiment of the invention, 7

the covered unit is vacuum baked and a suitable heat transfer liquidsuch as silicone oil is introduced through a pin hole in the covermember to fill the space between it and the transistor components. Afterfilling, the pin hole is sealed. Alternately, the cover member as may beturned upside down and filled with a predetermined amount of heattransfer liquid and the partially assembled transistor lowered into itand then the cover member suitably afiixed. However, certain embodimentsof the invention are used in applications where the amount of heat to bedissipated during operation is not great enough to require the presenceof a heat transfer liquid in the unit.

Subsequent to etching and washing and before attachment of the covermember 46, the transistor in its partially assembled condition is testedfor its electrical and other characteristics. If a particular unit isfound defective, the subassembly 17 can subsequently be separated fromthe header 11 simply by heating to melt the solder and lifting thesubassembly off the posts. The header, which forms the most expensivesingle part of the transistor, can then be reused with anothersemiconductor die unit and need not be discarded. In other transistorconstructions where the electrically operative parts of the transistorare of a construction and assembly less easily put together, and wherethe parts are welded to the header, it is diflicult to make thisseparation without damaging the header. In such instances, the headercannot be reused and must be scrapped thus adding materially to theoverall cost of the entire manufacturing operation.

With the transistor referred to as one embodiment of the presentinvention, the diminutive size can be more readily understood. Forinstance, in accordance with a typical embodiment, the header 11 isabout 0.345 inch in diameter at shoulder Ill) and includes mountingleads of 0.004 to 0.007 inch in diameter. The base connector 18 is about0.200 inch long and supports a semiconductor die about 0.060 inchsquare. Emitter bead 29 used to form an electrode in such embodiment is0.010 inch in diameter while collector bead 30 is 0.014 inch indiameter. FIG. 1 of the drawings is on a scale about four times as largeas a typical commercial unit. Of course, other sizes of electrodes,leads, etc. can be used by simple modifications in the assemblyequipment such as changing the size of the openings in the jig 33. Itcan readily be appreciated that the accurate and uniform alignment ofsuch minute parts would be difficult if not impossible to achievemanually. However, it is accomplished at a high rate of production bythe present invention.

The improved assembly method of the present invention, therefore,permits quick and accurate positioning of the various minute parts of asemiconductor device to be accomplished economically and consistently.In making an alloy junction transistor in accordance with the presentinvention, a high degree of control can be exercised over the extent ofelectrode alloying into the semiconductor die by providing independenttemperature control of the alloying of each electrode. Furthermore, theprocess is highly flexible in that it can be adapted to the manufactureof a wide variety of semiconductor devices of different electricalcharacteristics, thus providing for different customer requirements asthey arise in the application of such devices to circuits and electronicequipment.

As to the transistor structure of the present invention which iselectrically and mechanically stable, it is particularly suited toassembly by the rapid, easy and auto matic techniques of the method andapparatus herein disclosed. Because of the novel structure of thetransistor and its component parts, the latter are automatically andproperly aligned with one another during assembly to greatly increasethe effic'iency, to reduce the number of operators employed in contrastto a hand assembly, and to reduce the cost of manufacturing the devices.The transistor structure is particularly adapted for low and mediumpower applications, and can be used in conjunction with a wide varietyof semiconductor bodies and different types of alloyed junctions.Moreover, because of the configuration of the semiconductor subassembly,it can be easily and accurately afiixed to support posts of astandardized mounting header by soldering and can easily be removed fromthe header without injury to the latter if the subassembly is foundelectrically defective. The mounting header can then be reused withanother subassembly. This also efrects material manufacturing economies.

In all, therefore, the invention herein disclosed represents animportant improvement in the semiconductor art in that it providestechnical advances in methods and structures, and provides a commercialadvance in a lower cost stable device with very wide areas forapplication to equipment.

I claim:

1. A semiconductor device including in combination, a mounting headercomprising a body portion and first and second pairs of metallic postsheld in and extending above the upper surface of said body portion, saidsecond pair of posts having turned-over end portions, and a subassemblycomprising a metallic connector strip having a pair of arms and anextension portion between said arms with an edge thereof resting on theupper surface of the body portion of said header, a semiconductor bodycarried on said connector strip and lead wires extending from saidsemiconductor body, said lead wires resting on the turnedover portionsof said second pair of posts, apertured holding means at the end of eachof said arms interlocking with said first pair of posts, and solderconnections between said arms and said first pair of posts and betweensaid lead wires and the turned-over portions of said second pair ofposts, said apertured holding means and said turned-over posts and saidextension portion of said connector strip being so constructed andarranged to facilitate positioning of said subassembly on said headerand to hold said subassembly against movement relative to said headerduring a part of the assembly of said device before making said solderedconnections.

2. A semiconductor device including in combination, a mounting headercomprising a body portion and first and second pairs of metallic postsheld in and extending above the upper surface of said body portion, anda subassembly comprising a connector strip having a pair of arms and anextension portion between said arms with an edge portion thereof restingon the upper surface of the body portion of said header, a semiconductorbody carried on said connector strip in a position offset from thecenter thereof and lead wires extending from said semiconductor body,said second pair of posts having end portions turned over toward the endof said connector toward which said semiconductor body is offset,apertured holding means at the end of each of said arms interlockingwith said first pair of posts, and solder connections between said armsand said first pair of posts and between said lead wires and said secondpair of posts, said apertured holding means and said metallic posts andsaid extension portion of said connector strip being so constructed andarranged as to facilitate positioning of said subassembly on said headerand to hold said subassembly against movement relative to said headerduring a part of the assembly of said device and before making saidsolder connections.

3. A semiconductor device including in combination, a mounting headercomprising a body portion and first and second pairs of metallic postsheld in and extending above the upper surface of said body portion, anda subassembly having a shorter arm and a longer arm and an extensionportion between said arms with an edge portion thereof resting on theupper surface of the body portion of said header, a semiconductor bodymounted on the extension portion of said connector, lead wires extendingfrom said semiconductor body, said second pair of posts having endportions turned over toward the shorter arm of said connector andforming an acute angle with the upper surface of said body portion ofsaid header, apertured holding means at the end of each of said armsengaging said first pair of posts and solder connections between saidarms and said first pair of posts and between said lead wires and saidsecond pair of posts, said apertured holding means and said metallicpost and said extension portion of said connector strip being soconstructed and arranged as to facilitate positioning of saidsubassembly on said header and to hold said subassembly against movementrelative to said header during a part of the assembly of said devicebefore making said solder connections.

4. A semiconductor device including in combination, a mounting headercomprising a body portion and first and second pairs of metallic postsheld in and extending above the upper surface of said body portion, saidsecond pair of posts having turned over end portions with respect to theupper surface, a subassembly comprising a metallic connector striphaving a pair of arms and a widened portion between said arms, saidwidened portion having a curved edge resting on the upper surface of thebody portion of said header, a semiconductor body carried on saidwidened portion, and a pair of lead wires secured to and extending fromsaid semiconductor body, solder connections between said arms and saidfirst pair of posts and between said lead wires and the turned overportion of said second pair of posts, means at the ends of said armsengaging said first pair of posts and cooperating With said posts tofacilitate positioning of said subassembly with respect to said posts inthe original assembly of the subassembly thereon and to thereafterretain said subassembly against lateral movement during establishment ofsaid solder connections, said lead wires being adapted to movedownwardly along said turned portions of said second pair of posts andsaid connector being so constructed and arranged as to turn along saidcurved edge during establishment of said solder connections so that saidsubassembly tends to settle to a stable mounting position on said headerduring assembly of said device.

5. A semiconductor device including in combination, a mounting headercomprising a body portion and first and second pairs of upstandingmetallic posts held in and extending above the upper surface of saidbody portion, said second pair of posts having turned-over end portions,and a preassembled self-jigging subassembly soldered to said. posts,said subassembly comprising a connector strip having a pair of arms,apertured holding portions at the ends of each of said arms engaging oneof said first pair of posts, a semiconductor body carried on saidconnector strip, and lead wires extending from opposite sides of saidbody and resting on said turned-over end portions of said second pair ofposts with an edge portion of said connector strip resting on the uppersurface of the body portion of said mounting header.

6. In a semiconductor device' which includes a semiconductor die unit, amounting and connection system Which serves positioning functions in theassembly of the device and provides mechanical connections andelectrical connections in the completed device, said mounting andconnection system including in combination a base, conductive mountingposts supported by said base and projecting from one side thereof,connector means having a portion on which the semiconductor die unit iscarried in a position above said base and including first and secondconnector arms projecting from such portion, said connector arms eachhaving an apertured mounting portion fitting about a respective mountingpost and interlocking said arm with said posts, connector Wiresconnected to the semiconductor die unit and extending to respective onesof said mounting posts, with said last-named mounting posts beingturned-over with respect to said base to receive and retainsaidconnector Wires thereon in the assembly of the device, and solderconnections between each said connector Wire and connector arm and thecorresponding mounting post.

References @ited in the file of this patent UNITED STATES PATENTSMcLaughlin May 6, 1952 2,796,563 Ebers et al. June 18, 1957 2,810,873Knott Oct. 22, 1957 2,825,014 Willemse Feb. 25, 1958 2,845,375 Gobat eta1 iuly 29, 1958 2,981,875 Kelley et a1 Apr. 25, 1961 3,028,663

IWersen et a1. Apr. 10, 1962

5. A SEMICONDUCTOR DEVICE INCLUDING IN COMBINATION, A MOUNTING HEADERCOMPRISING A BODY PORTION AND FIRST AND SECOND PAIRS OF UPSTANDINGMETALLIC POSTS HELD IN AND EXTENDING ABOVE THE UPPER SURFACE OF SAIDBODY PORTION, SAID SECOND PAIR OF POSTS HAVING TURNED-OVER END PORTIONS,AND A PREASSEMBLED SELF-JIGGING SUBASSEMBLY SOLDERED TO SAID POSTS, SAIDSUBASSEMBLY COMPRISING A CONNECTOR STRIP HAVING A PAIR OF ARMS,APERTURED HOLDING PORTIONS AT THE